By: CJ

Understanding how passkeys work starts with public-key cryptography. Instead of sending a password to a website, a passkey uses a pair of cryptographic keys to verify a user’s identity. The private key stays protected by the user’s authenticator, while the website uses the corresponding public key to confirm that the sign-in is legitimate.

Passwords have been the standard way to protect online accounts for decades, but they have a persistent weakness: they depend on users keeping a secret that can be guessed, reused, stolen, or entered on a fraudulent website. Even a long password can become a security risk if it is exposed in a data breach and reused elsewhere.

Understanding how passkeys work helps explain why a different approach to signing in is gaining attention. Instead of requiring users to type a password each time, passkeys use cryptographic keys to verify identity, often through a fingerprint, facial recognition, or a device PIN. They can make signing in both simpler and more resistant to common attacks, but how much safer are they than passwords in practice?

Passkeys are increasingly supported by websites, apps, and operating systems. Instead of asking users to remember a secret, they use cryptographic keys and a device-based verification process. A person might approve a sign-in with a fingerprint, facial recognition, or their device’s PIN, depending on the system they use.

This makes passkeys more convenient, but convenience is only part of their appeal. Their underlying design addresses several common weaknesses of passwords, particularly phishing and password reuse. However, passkeys are not a guarantee against every form of account compromise. Understanding how they work, where their protection comes from, and what happens if a device is lost can help people decide when to use them.

What Is a Passkey?

A passkey is a digital credential that allows someone to sign in to a specific website or app without entering a traditional password. It is based on public-key cryptography, a system that uses two mathematically related keys rather than relying on a secret that both the user and the service must share.

When a passkey is created, a unique key pair is generated for the account. The private key is held by the user’s authenticator, which may be a phone, computer, security key, or credential manager. The public key is registered with the website or service. The two keys work together to verify the user’s sign-in without requiring the private key to be sent to the website.

The process is designed to be simple from the user’s perspective. Instead of typing a password, the person selects their account and confirms their identity using an available method, such as a fingerprint, facial recognition, or device PIN. The exact steps depend on the device, operating system, and service.

It is important to understand that a passkey is not the same thing as a fingerprint or face scan. Biometrics may be used to unlock or authorize the credential on a device, but the passkey itself is the cryptographic credential used to authenticate with the service. This distinction helps explain why passkeys can work across different devices and verification methods.

How Passkeys Work: A Step-by-Step Explanation

Passkeys replace the usual exchange of a password with a cryptographic verification process. Although the technical details happen in the background, the basic sequence is straightforward.

1. The device creates a pair of keys

When a user registers a passkey with a supported website or app, the authenticator creates a public and private key pair. The keys are unique to that account and service. The private key remains protected by the authenticator, while the public key is provided to the service during registration.

This arrangement differs from a conventional password system. A website normally needs to verify a password or a value derived from it. With passkeys, the service can verify a cryptographic signature using the public key without storing the private key itself.

2. The website requests proof of identity

When the user returns to sign in, the service sends a challenge: a value that the authenticator must respond to in a way that proves it holds the correct private key. The authenticator may ask the user to unlock their device or approve the action first.

The authenticator then uses the private key to sign the challenge. The website checks the signature using the registered public key. If the signature is valid and the other required checks succeed, the service can authenticate the user.

The private key is not sent to the website during this exchange. This is a major security difference because the server does not need to receive the secret credential itself to verify a sign-in.

3. The user confirms the sign-in

From the user’s perspective, the final step may involve touching a fingerprint sensor, looking at a camera, entering a device PIN, or approving a prompt. These methods help ensure that someone with access to the device cannot automatically use every stored credential without authorization.

The exact method depends on the authenticator and the service’s requirements. Some sign-ins may require a separate device or an additional confirmation step. The important point is that the verification method unlocks or authorizes use of the passkey; it is not itself the cryptographic key.

Why Are Passkeys Safer Than Passwords?

Passkeys are designed to reduce several risks associated with traditional password-based sign-ins. Their strongest advantages come from how they are created, how websites verify them, and how they are tied to specific services.

They are resistant to phishing

Phishing happens when someone tricks a user into revealing credentials through a fake login page, message, or website. A convincing imitation of a real service can capture a password even if that password is long and complicated.

Passkeys help prevent this type of theft because the credential is associated with the identity of the website or app for which it was created. The browser and authenticator check that identity as part of the sign-in process. A passkey registered for a legitimate website should not be usable by a lookalike domain simply because the page looks convincing.

This removes an important decision from the user. With passwords, people must recognize a fraudulent page before entering their credentials. With passkeys, the authentication system checks the site’s identity, making it substantially harder for a phishing page to collect a reusable login secret.

Passkeys do not eliminate every phishing risk. Attackers can still use deceptive messages to target account recovery, persuade people to approve other actions, or compromise devices. However, passkeys provide stronger protection against credential-harvesting attacks than passwords alone.

They cannot be reused across unrelated websites

Password reuse is a common security problem. Someone might use the same password for email, shopping, social media, and several other accounts because remembering a unique password for every service is difficult. If one company suffers a data breach, attackers may try the exposed credentials on other websites. This is known as credential stuffing.

Passkeys are created for individual accounts and services rather than being human-chosen strings that can be copied from one login page to another. A passkey for one website cannot simply be typed into a different website to access another account.

This helps limit the impact of a breach at an unrelated service. It also removes the burden of inventing and remembering a different strong password for every account.

A website does not store the private key

A service that supports passkeys stores the public key needed to verify authentication, not the user’s private key. If the service’s database is stolen, the exposed public keys alone cannot be used to generate the private keys or sign in as users.

This reduces the value of stolen authentication databases compared with databases containing password material that attackers may be able to crack or exploit. It does not mean a breach is harmless: attackers could still target other account information, exploit weaknesses in a service, or interfere with account records. Passkeys reduce a specific category of risk rather than preventing all possible server-side attacks.

Users do not have to create strong passwords

A password’s security depends partly on how it is chosen. Short, predictable, or reused passwords are easier to exploit than long, unique ones. Passkeys are generated by the authentication system rather than invented by the user, so they do not suffer from weak password choices in the same way.

This can improve security without requiring people to remember complicated strings or rely entirely on their own password habits. It also reduces the need to type credentials into public or shared environments.

Are Passkeys Completely Secure?

No authentication method is completely secure. Passkeys address important weaknesses in passwords, but the overall security of an account still depends on the device, the credential manager, the service, and the ways users can recover access.

For example, a person whose phone is stolen may face a risk if the device is already unlocked or its screen lock is weak. Someone who gains control of a user’s broader account or credential manager may also create problems, depending on how passkeys are stored and synchronized. Malware and compromised devices can introduce risks that passkeys alone cannot solve.

Account recovery is another important consideration. If a service allows a user to regain access through a weak recovery process, an attacker may attempt to exploit that process instead of attacking the passkey directly. Email accounts, recovery codes, backup methods, and support procedures can therefore remain important parts of account security.

Passkeys should be understood as a stronger way to authenticate, not as a replacement for every other security measure. Users should still secure their devices, keep software updated, protect their primary email and credential-manager accounts, and review account recovery options.

What Happens If You Lose Your Phone?

Losing a phone does not necessarily mean losing every passkey. What happens depends on where the passkeys are stored and whether they are available through another device or a supported synchronization service.

Synced passkeys

Some passkeys can be securely synchronized across a user’s devices through a supported credential manager. If a phone is lost, the user may be able to access the same passkey from another device after signing in to the relevant credential-manager account and completing its security checks.

This is convenient, but it makes protecting that account especially important. Users should understand which service stores their passkeys and how to recover access if they lose their main device.

Device-bound passkeys

Other passkeys are tied to a particular device or physical security key rather than being synchronized through a cloud-based credential manager. These can be useful in situations where an organization or user wants the credential to remain on a specific authenticator. However, losing that device may make the passkey unavailable.

For important accounts, users should check whether they can register another passkey or use a supported backup sign-in method. It is better to understand the recovery process before losing access than to discover its limitations during an emergency.

What should you do if a device is stolen?

If a device containing passkeys is lost or stolen, use another trusted device to review the affected accounts. Where available, sign out the lost device, remove its passkeys or sessions, and follow the service’s instructions for securing the account. If the device may have been accessible to someone else, change relevant account credentials and review recovery settings as appropriate.

The exact steps vary by service. For this reason, users should not assume that every passkey is automatically backed up or that deleting one from a website necessarily removes every copy stored in a separate credential manager.

Passkeys vs. Passwords: What Is the Difference?

Passkeys and passwords both allow services to verify a user’s identity, but they approach authentication differently.

Feature	Passkeys	Passwords
How users sign in	Approve a cryptographic credential, often using a device PIN or biometrics	Enter a secret string
Phishing protection	Designed to resist phishing through website-bound authentication	Can be stolen on convincing fake login pages
Reuse across websites	Each passkey is associated with a particular service and account	Users may reuse the same password across services
Server-side credential	Service stores a public key for verification	Service stores password-related verification data
Remembering credentials	Usually managed by a device or credential manager	Users must remember them or use a password manager
Recovery	Depends on synchronization, backup authenticators, and service recovery	Depends on password reset and account recovery options
Availability	Only works where supported	Supported by almost all traditional login systems

For most people, the key difference is not that passwords can never be secure. A unique, long password stored in a reputable password manager can be a strong defense. The problem is that passwords remain vulnerable to phishing, reuse, and mistakes during login. Passkeys are designed to reduce those risks at the authentication level.

Should You Switch to Passkeys?

If a website or app you use supports passkeys, they are generally a good option to consider, especially for important accounts. They can make sign-ins easier while reducing exposure to several common password attacks.

Start with accounts that matter most, such as your primary email, financial services where passkeys are supported, and accounts that control access to other services. Before making a change, confirm how the service handles backup access and what happens if your phone or computer becomes unavailable.

It is also sensible to keep your devices protected with a strong screen lock and to use a supported credential manager you trust. If passkeys are synchronized through an account, secure that account carefully and make sure you understand its recovery process. For particularly important accounts, consider registering a second passkey or another supported authenticator when the service allows it.

You do not need to switch every account at once. Some services still rely on passwords, and certain accounts may offer different authentication options depending on the device or operating system. You can use passkeys where they are supported while maintaining unique passwords and a reputable password manager for accounts that still require them.

The Bottom Line

Passkeys are a meaningful improvement over traditional passwords because they replace a reusable secret with a cryptographic credential tied to a particular service. They are designed to resist phishing, prevent password reuse across unrelated sites, and reduce the risk associated with stolen website credential databases. They can also make everyday sign-ins simpler by using a device’s existing security features.

However, passkeys do not remove every security risk. Device theft, compromised credential managers, weak recovery processes, and other account-security problems still matter. Before relying on passkeys for important accounts, users should understand where their credentials are stored and how they can recover access if a device is lost.

For most users, the practical approach is to adopt passkeys on important services when available, keep devices and recovery accounts secure, and retain a reliable backup plan. They are not a guarantee of perfect security, but they offer a stronger and often more convenient way to protect online accounts.

Sources and Further Reading

• MDN Web Docs: Passkeys — an overview of passkeys, public-key cryptography, and phishing resistance.
• FIDO Alliance: Passkeys — background on passkey standards, device-bound and synced credentials, and cross-device sign-in.
• Google for Developers: Passkeys — an explanation of passkey security and how public-key cryptography is used.
• National Cyber Security Centre: Passkeys — What You Need to Know — practical security guidance on using passkeys instead of passwords.